McDonald’s, Just Eat and Deliveroo are among the brands speaking to TfL, according to the The Sunday Times. The paper also reported that some brands were considering legal challenges.

A McDonald's spokesman said the brand had engaged in "constructive conversations" with TfL and intended to fully comply with the change of policy, adding it had no plans to make a legal challenge.

The spokesman said: "When it comes to advertising and marketing, we have always taken our responsibilities extremely seriously. We never advertise products considered to be high in fat, salt or sugar to children and are already in the process of changing our directional adverts in London which signpost nearby restaurants.

"Because of the choice we offer and the proactive changes we have made to our menu over many years, our customers in London will continue to see our adverts when travelling on the TfL network. McDonald’s has a long and proud history in the capital and we are committed to working in partnership with the Mayor to help ensure Londoners always have access to affordable, good food."

Deliveroo told the Sunday Times it has had "very positive engagement with TfL ahead of the incoming changes". Just Eat said it was "exploring options" to allow the company to keep advertising under the new rules.

The new regime follows a public consultation that began in May and attracted 1,500 responses.

Khan claimed last month that 82% of responses supported the proposals, which have been backed by NHS England and the Royal College of Paediatrics and Child Health.

He said: "It’s clear that advertising plays a huge part in the choices we make, whether we realise it or not, and Londoners have shown overwhelming support for a ban on ads for junk food and drink on our transport network.

"It’s completely unacceptable that, in a city as prosperous as London, where you live and the amount you earn can have a massive impact on whether you have access to healthy, nutritious food. I’m determined to change this."